Our studies in the past year have indicated that in the absence of sodium, ouabain binds to a receptor site in the sartorius muscle that enhances oxygen uptake following membrane depolarization by raising external K plus O to 20 micromolar. We have also noted that under these conditions ouabain potentiates a potassium induced contracture (80 micromolar K plus O). We will determine the binding of ouabain to sartorius muscles as a function of Na plus O and Ca2 plus O to determine if binding kinetics can demonstrate two high affinity binding sites -- one related to the Na-K transport system, the other related to the enhancement of calcium release from the sarcoplasmic reticulum by membrane depolarization. We will measure the effect of potassium depolarization and low concentrations (0.5 micromolar of caffeine and SQ20.009 on c-AMP and c-GMP levels in frog sartorius muscles with and without "glycerol treatment". We wish to determine if the enhancement of oxygen uptake by increasing K plus O is indeed associated with a rise in c-GMP and if caffeine specifically increases c-GMP levels in muscle. The measurements of c-GMP and c-AMP in "glycerol-treated" muscles should enable us to determine if the biochemical leision produced under such treatment is related to either the c-GMP or c-AMP systems. Finally, we will determine the effects of c-GMP on calcium binding to the surface membrane of single barnacle fibers. Bibliographic references: Dawson, M.J. and Bianchi, C.P. Restoration of potassium-stimulated respiration of "Glycerol-Treated" muscle. European J. of Pharmacology, 30: 288-297, 1975; Bianchi, C.P., Narayan, S. and Lakshminarayanaiah, N. Mobilization of muscle calcium and oxygen uptake in skeletal muscle. Current topics an Intracellular Regulation: First International Symposium on Calcium Transport in contraction and secretion. Bressonon (Brexin) May 11-16, 1975. Excerpta Medica Foundation Amsterdam, The Netherlands.